Many light sources for general illumination, such as linear fluorescent fixtures and some parabolic aluminized reflector lamps, typically have a fixed angular distribution of light that is a property of the light source. For instance, if a particular fixed-width light fixture is designated as having a “wide” beam, the fixture generally cannot be adjusted easily to produce a “narrow” beam.
An improvement to the fixed-width fixture is an adjustable-width fixture. Typically, these fixtures rely on mechanical movement to produce a change in the width or distribution of the output beam. For instance, moving a source relative to a reflector or a lens may produce a change in the output beam width. As another example, an adjustable aperture or iris may be used to block light that falls outside a desired beam width.
These known adjustable-width fixtures may have several disadvantages. First, they may be prone to failure because they include moving parts, which can wear with time. Second, they may be inconvenient to adjust because they may be out of reach. Third, for the case of the iris that blocks the periphery of the output beam, a significant fraction of the output light may be wasted.
Accordingly, there exists a need for a light fixture that has the flexibility to adjust its output beam profile, but overcomes the disadvantages stated above.